Conventionally, the braking apparatus capable of braking the vehicle during travel is provided on the vehicle, and the braking apparatus is to generate required braking force required by a driver to the braking apparatus by operation of the brake pedal by the driver in wheels of the vehicle. Such braking apparatus includes a so-called brake-by-wire system and an in-line system. There is the brake-by-wire system and the in-line system composed of a hydraulic brake system for generating the pressure braking force by action of a wheel cylinder pressure to a wheel cylinder, which allows a brake pad to contact a brake rotor, by application of the pressure to brake oil, which is the working fluid, according to the operation of the brake pedal operated by the driver, and a regenerative braking apparatus for generating regenerative braking force by performing the regenerative braking. The braking apparatuses generate the required braking force according to the operation of the brake pedal by the driver by the pressure braking force generated by the hydraulic brake apparatus and the regenerative braking force generated by the regenerative braking force.
The brake-by-wire system is, for example, to detect an amount of displacement according to the operation of the brake pedal operated by the driver such as a pedal stroke amount of the brake pedal by a stroke sensor, and drive a pressurizing pump provided on the hydraulic brake apparatus based on the detected pedal stroke amount, thereby allowing the wheel cylinder pressure to act on the wheel cylinder to generate the pressure braking force. That is to say, in the brake-by-wire system, the brake pedal and the hydraulic brake apparatus are not basically directly coupled to each other. Although such brake-by-wire type braking apparatus is capable of high-accuracy cooperative control, there is a problem that this is expensive.
On the other hand, the in-line system is to pressurize the brake oil by a master cylinder provided on the hydraulic brake apparatus, according to the operation of the brake pedal operated by the driver, and supply the brake oil stored in the reservoir to the wheel cylinder, thereby allowing a master cylinder pressure, which is the pressure of the master cylinder, to act on the wheel cylinder as the wheel cylinder pressure and generating the master pressure braking force based on the master cylinder pressure as the pressure braking force. That is to say, in the in-line system, the brake pedal and the hydraulic brake apparatus are basically directly coupled to each other. Also, the in-line system is provided with a pressurizing pump for further pressurizing the brake oil by the pump or the like to apply a pressurized pressure to the brake oil, for example, when the required braking force may not be generated by the pressure braking force generated by the wheel cylinder pressure acting on the wheel cylinder only by the pressurization of the brake oil by the master cylinder, that is to say, by a sum total of the master pressure braking force and the regenerative braking force. That is to say, the wheel cylinder pressure to act on the wheel cylinder is the total pressure of the master cylinder pressure and the pressurized pressure, and the generated pressure braking force is the sum total of the master pressure braking force and the pressurized braking force.
As such conventional in-line system braking apparatus, for example, a vehicle braking apparatus described in the Patent Document 1 is provided with a fluid-pressure braking apparatus capable of applying a control fluid pressure to be formed while driving the pump irrespective of the brake operation to the wheel cylinder and applying control fluid-pressure braking force to the wheel corresponding to the wheel cylinder, a regenerative brake apparatus for generating the regenerative braking force corresponding to a brake operating state detected by brake operating state detecting means for detecting a state of brake operation on the wheel by a motor for driving any of the wheels, and braking force compensating means for compensating deficiency of the braking force due to variation of the regenerative braking force. By doing this, the vehicle braking apparatus described in the Patent Document 1 makes the fluid-pressure brake apparatus smaller and light weight, and when the regenerative braking force by the regenerative brake apparatus varies, this compensates the deficiency of the braking force due to the variation by the fluid-pressure braking force by the fluid-pressure brake apparatus.    Patent Document 1: Japanese Patent Application Laid-open No. 2006-21745